LECTURE 2: MEMBRANES, CHANNELS & TRANSPORT Flashcards
1
Q
- separates the cytoplasm from the external
environment - one of the most important cell organelles
- a highly selective permeable barrier that
surrounds all living cells - controls how molecules and compounds
move in and out of the cell - very important for proper nutrition,
maintenance of irritability of the cells, and
homeostasis - define boundaries and serve as permeability
barriers - surrounds all
animal cells - extraordinary thin
(6-23 nm) - lipid-based
structure that
encloses the cytosol
A
CELL MEMBRANE
2
Q
Cell Membrane a _______ _______ _______barrier that surrounds all living cells
A
highly selective permeable
3
Q
Cell Membrane is Important for
A
-proper nutrition,
-maintenance of irritability of the cells, and
-homeostasis
-signal detection
-cell to cell communication
-compartmentalization
4
Q
Cell membrane is extraordinary thin, around _____
A
6-23 nm
5
Q
Cell membrane sustains different concentrations of certain ions on
their two sides, leading to _____________
A
concentration gradient
6
Q
__________ participates in the transport of substances
A
protein structures
7
Q
- describes the organization of cell
membranes - phospholipids drift and move like a fluid
- bilayer is a mosaic mixture of
phospholipids, steroids, proteins, and
other molecules
A
The Fluid Mosaic Model
8
Q
Cell membrane is composed of _________, ________, ____________ and are arranged in a _____ ______ structure.
A
-phospholipids, proteins, and
carbohydrates
-Fluid Mosaic
9
Q
Cell Membrane is composed of _______ and ________ molecules kept together by non-covalent interactions and mostly “_______” in the plane of the bilayer.
A
- Lipid and Proteins
-Float
10
Q
lipid and protein molecules kept
together by ______________________
A
non-covalent interactions
11
Q
impermeable to the passage of
most water-soluble molecules
A
Lipid Bilayer
12
Q
fundamental structure of the
membrane
A
Lipid Molecules
13
Q
- inside surface maintain cell shape or cell
motility - enzymes - catalyzing reactions in the
cytoplasm. - act as receptors (specific binding site
where hormones or other chemicals can
bind; used for cell signaling and cell
recognition)
usually span from one side of the
phospholipid bilayer to the other (integral
proteins), but can also sit on one of the
surfaces (peripheral proteins) - can slide around the membrane very
quickly and collide with each other, but
seldom flip from one side to the other - responsible for most of the membrane’s
properties
A
Proteins
14
Q
embedded in the lipid bilayer
provide a mechanism for trans-membrane
transport
A
Integral Proteins
15
Q
Integral proteins embedded in the lipid bilayer provide a mechanism for trans-membrane
transport, includes:
A
-passive-transport pores and channels,
-active-transport pumps and carriers, membrane-linked enzymes,
-chemical signal receptors
-transducers
16
Q
associated with the
surface of the membrane via electrostatic
interaction
A
Peripheral Proteins
17
Q
Peripheral proteins are associated with the
surface of the membrane via_________
A
electrostatic
interaction
18
Q
Proteins inside surface maintain ________ or ______
A
Cell shape or Cell Motility
19
Q
Proteins acts as _______ catalyzing reactions in the cytoplasm.
A
Enzymes
20
Q
Proteins acts as receptors that acts as the specific binding site where ___________ and other__________ can bind, used for __________ and ________
A
- hormones or other chemicals
-cell signaling and cell recognition
21
Q
proteins in the plasma membrane may provide
a variety of major cell functions, this includes:
A
-Transport
-Enzymatic Activity
-Signal Transduction
- Intercellular Joining
-Cell-cell communication
-Attachment to the cytoskeleton and extracellular matrix
22
Q
Each type of protein in a membrane has a
special function, including:
A
-Adhesion Protein
-Recognition Protein
-Receptor Protein
-Enzymes
-Transport Protein (active and passive)
23
Q
-found on the outer surface and attached
to the proteins or sometimes to the
phospholipids
-form a cell coat or glycocalyx outside the
cell membrane
A
Carbohydrates
24
Q
___________ is responsible for Maintaining the cell stability and cell recognition and is attached to the lipids
A
Glycolipids
25
bear oligosaccharide side chains
and are vital for cell recognition and
communication, attached to the protein
Glycoproteins
26
_______ is used for protection and cell
recognition
Glycocalyx
27
What are the primary types of lipids
1. Phosphoglycerides
2.Spingholipids
3. Sterols
28
glycerol backbone
Phosphoglycerides
29
backbone
made of sphingosine
bases
Sphingolipids
30
cholesterol,
nonpolar and only slightly
soluble in water
Sterols
31
one end is hydrophilic –
water soluble; other end is
hydrophobic – water
insoluble
amphipathic
32
*amphipathic
(one end is hydrophilic –
water soluble; other end is
hydrophobic – water
insoluble)
* dual nature is crucial to the
organization of biological
membranes
* self-repairing
* differences in the lengths of
the two fatty acid tails and
their composition influence
fluidity
phosphoglycerides and sphingolipids
33
*lateral movement of lipids and proteins within a surface of the bilayer is very common
* depends on its composition and cholesterol
(binds weakly to phospholipids making the
membrane less fluid but stronger)
Membrane Fluidity
34
________________ of lipids and proteins within a surface of the bilayer is very common
lateral movement
35
binds weakly to phospholipids making the
membrane less fluid but stronger
Cholesterol
36
membrane molecules are held in place by
relatively _______________________
weak hydrophobic interactions
37
most lipids and some proteins can drift laterally in the plane of the membrane, but rarely ______ from one layer to the other
flip-flop
38
influenced by
temperature and
constituents
Membrane Fluidity
39
decreased temperature, membrane fluid state turns ________ where phospholipid are more closely packed.
solid state
40
* wedged between phospholipid molecules in
the plasma membrane of animals cells.
* at warm temperatures, it restrains the
movement of phospholipids and reduces
fluidity
* at cool temperatures, it maintains fluidity by
preventing tight packing
Steroid Cholesterol
41
At _________________, steroid cholesterol restrains the
movement of phospholipids and reduces
fluidity
Warm temp
42
At ___________________, steroid cholesterol maintains fluidity by
preventing tight packing
Cool Temp
43
* freeze-etch electron
micrographs of the
surface of a membrane
shows the progressive
removal of
* proteins when subjected
to digestion with
proteolitic enzyme
Membrane Heterogeneity
44
* splits a membrane
along the middle of
the phospholid bilayer
prior to electron
microscopy.
* shows protein
particles interspersed
with a smooth matrix,
supporting the fluid
mosaic model.
Freeze Fracture
45
* regulates the passage of materials (gases,
nutrients, wastes) in and out of the cell
* hydrophobic interior makes membranes
highly impermeable to most polar
molecules
Selective permeability
46
* The rate at which a substance can
passively penetrate a cell membrane
* Influenced by inherent properties of both
the membrane and the substance
Membrane permeability
47
What are the two transport systems?
-Passive Processes
-Active Transport
48
* no energy expenditure and move down
their normal gradient
Passive Transport
49
Types of Passive Transport
* simple diffusion/lipid diffusion
* osmosis
* facilitated diffusion/passive Transport
50
What are the three basic routes
1. Dissolving in Lipid Phase
2. Diffusion through labile or fixed aqueous
channels
3. Carrier mediated transport (facilitated or
active transport)
51
* molecules diffuses through the membrane
* diffusion and osmosis
*leaves the aqueous phase on one side of the
membrane
* dissolves directly in the lipid bilayer
*diffuses across the thickness of the lipid or protein
layer
*enters the aqueous phase on the opposite side
Dissolving in lipid phase
52
* solute molecule remains in the aqueous phase
*diffuses through aqueous channels (water-filled
pores in the membrane)
Diffusion through labile or fixed aqueous
channels
53
* solute molecule combines with a carrier
molecule dissolved in membrane
*carrier “mediates” or “facilitates” the
movement of the solute molecule across the
membrane
Carrier mediated transport (facilitated or
active transport)
54
-random thermal motion of suspended
or dissolved molecules causes their dispersion
from regions of higher concentration to regions of
lower concentrations
-Net movement of particles (atoms, molecules,
or ions) along a concentration gradient from
an area of higher concentration to an area of
lower concentration
Diffusion
55
Diffusion is the random thermal motion of suspended
or dissolved molecules causes their dispersion
from______________________________________
regions of higher concentration to regions of
lower concentrations
56
Diffusion: Net movement of ________
Particles
57
movements of individual molecules are
________
random
58
In the absence of other forces, a substance will
diffuse from where it is_______________________________
more concentrated to
where it is less concentrated (down its
concentration gradient)
59
Each substance diffuses down its_____________________, independent of the
concentration gradients of other substances
own
concentration gradient
60
diffusion of a substance across a biological
membrane is ____________________-
passive transport (exergonic)
61
assist molecules with
limited permeability to diffuse through the lipid
bilayer
Transport Proteins
62
* Net diffusion rate across a fluid membrane is
proportional to the difference in partial
pressure, proportional to the area of the
membrane and inversely proportional to the
thickness of the membrane
Fick’s Law of Diffusion
63
Fick’s Law of Diffusion: Formula
J = - DA (∆C/∆ X)
64
______________of a membrane to a substance
is the rate at which that substance passively
penetrates the membrane under a specified
set of conditions
Permeability
65
INTRINSIC FACTORS GOVERNING DIFFUSION
ACROSS MEMBRANES:
* Size rule (Ex. water > urea)
* Polarity rule (Ex. Hexane - non polar > ethanol
polar)
* Ionic rule (Ex. O2 > -OH)
66
* a few substances can diffuse directly through
the lipid bilayer part
* lipid-soluble molecules such as steroids, or
very small molecules, such as H2O, O2 and CO2
Simple Diffusion/Lipid Diffusion
67
Rate of diffusion depends on five
factors:
◦ Size
◦ Temperature
◦ Steepness of the concentration gradient
◦ Charge
◦ Pressure
68
Factors that influence mobility of solute molecule
1. Lipid Solubility
2. Hydrogen Bond with water
3. Molecular Weight
4. Molecular Shape
5. Partition coefficient
69
With increasing solubility the mobility increase
Lipid Solubility
70
Increase in hydrogen bond with water decreases mobility
Hydrogen bond with water
71
ratio of the distribution of a
substance between two different liquid phases
(e.g. oil and water)
Partition coefficient
72
Partition Coefficient: Formula
K = solute concentration in lipid/
solute concentration in water
73
Passive Diffusion: rate of influx increases in proportion to the
concentration of the solute in the extracellular
fluid (difference in the number of solute
molecules on the two sides of the plasma
membrane
Non- saturation Kinetics
74
diffusion of water across a selectively
permeable membrane is a special case of
passive transport called ________
Osmosis
75
Osmosis continues until the solutions are _________
isotonic
76
Osmosis: water moves from ______________________________
(down its concentration gradient)
higher to lower water potential
77
the movement of water can produce a ____________ (a fluid mechanical pressure), resulting in a
pressure gradient across a semipermeable
membrane
hydrostatic
pressure
78
Hydrostatic Pressure
A fluid mechanical pressure
79
Osmosis pertains to solvent particles; determined by __________
Osmotic Pressure
80
the difference in hydraulic
pressures of a solution and water (interfacing one another at either side of an SPM) which must be overcome to prevent the entry of water into the solution across the membrane
Osmotic Pressure
81
Osmotic Pressure is described by _________
Van t’Hoff equation
82
Van t’Hoff equation
π = Φn (C/M)R
83
when two aqueous solutions exert
the same osmotic pressure through a
membrane permeable only to water.
Isosmotic
84
if one solution exerts less
osmotic pressure than the other
Hypoosmotic
85
if one solution exerts greater
osmotic pressure than the other
Hyperosmotic
86
the concentration of a solution
expressed as the total number of solute particles
per liter
Osmolarity
87
response of cells or tissues
immersed in the solution
Tonicity
88
–osmotic pressure property of a solution
Osmoticity
89
no osmotic pressure
difference between the cell and interior and the
extracellular solution; no net water gain;
cell/tissue neither shrinks nor swell.
*Isotonic solution
90
If the tissue swells because it absorbs water,
the solution is _______ to the tissue.
hypotonic
91
If the tissue shrinks because it loses water, the
solution is ______ to the tissue
hypertonic
92
_______________ depends on the balancing water uptake and loss
Cell Survival
93
What happen to animal cell and plant cell in Hypotonic Solution?
Animal Cell: Lysed
Plant Cell: Turgid (Normal)
94
Why does plant cell don't burst in hypotonic solution?
Because of the Cell Wall
95
What happen to animal cell and plant cell in Isotonic Solution?
Animal Cell: Normal
Plant Cell: Flaccid
96
What happen to animal cell and plant cell in Hypertonic Solution?
Animal Cell: Shriveled
Plant Cell: Plasmolyzed
97
* through transmembrane proteins
* transport proteins tend to be specific for one
molecule, so substances can only cross a
membrane if it contains the appropriate
protein
Facilitated Diffusion/ Passive Transport
98
Two kinds of transport protein
Channel and Carrier
99
*____________________ in the membrane
allows charged substances (usually ions) to
diffuse across membranes
water-filled pore or channel
100
most channels can be _____________, allowing the cell to control the entry
and exit of ions
gated (opened or
closed)
101
small organic compounds
that specifically transports ions across
the plasma membrane
Ionophores
102
some channel proteins, gated channels,
open or close depending on the ________________________
presence or
absence of a physical or chemical stimulus
103
transports a single solute from
one side of the membrane to the other
Uniporters
104
transfer one solute
and simultaneously or sequentially transfer a
second solute
Coupled transporters
105
-transfer solutes in the same
direction
-run on energy stored in
ion gradients
symporters
106
transfer solutes in opposite
directions
antiporters
107
Channel Mediated Transport: the rate of influx increases in proportion to the
concentration of the solute in the extracellular
fluid (difference in the number of solute
molecules on the two sides of the plasma
membrane
Saturation Kinetics
108
*binding site for a specific solute and
constantly flip between two states so that the
site is alternately open to opposite sides of
the membrane
*substance will bind on the side with higher
concentration and be released at the lower
concentration side
Diffusion through a carrier
109
binding site for a specific solute and
constantly flip between two states so that the
site is alternately open to opposite sides of
the membrane
Carrier
110
show saturation kinetics
Channel and carrier-mediated transport
111
*require metabolic energy
and moves substances against their gradients
* proteins are highly specific -
different protein pump for
each molecule to be
transported
* critical for a cell to maintain
its internal concentrations of
small molecules that would
otherwise diffuse across the
membrane.
* ATP supplies the energy for
most active transport
Active Transport
112
supplies the energy for
most active transport
ATP
113
actively maintains
the gradient of sodium (Na+) and potassium
ions (K+) across the membrane
Sodium-potassium pump
114
Important Features of Active Transport
1. Transport can take place against substantial
concentration gradient
2. Exhibits high degree of selectivity
3. ATP or other sources of energy are required
4. Certain membrane pumps exchange one kind of molecule or ion from one side of the membrane for another kind of molecule or ion from the other side
5. Some pumps perform electrical work by producing a net flux of charge
6. Selectively inhibited inhibited by specific blocking agents
7. Energy is released by the hydrolysis of ATP by enzymes (ATPases) present in the membrane
115
In _________, a membrane protein couples the transport of two solutes
Cotransport
116
A single ATP-powered pump that transports
one solute can indirectly drive the active
transport of several other solutes through
___________ via a different protein
cotransport
117
As the solute that has been actively
transported diffuses back passively through a
transport protein, its movement can be
______________________________ against its concentration gradient
coupled with the active transport of another
substance
118
Na+ /H+ antiporter in
the proximal tubule of the
mammalian kidney
- for each H+ expelled, one Na+ is
taken up into the cell
- advantages: avoiding the
expenditure of energy to perform
electrical work (two equivalent +
charges are exchanged)
- enables the kidney to reclaim
Na+ from urine and excess protons
Antiporters
119
No Energy, No Proteins, No Specific, Not controllable
Lipid Diffusion
120
No Energy, No Proteins, Yes Specific, Not Controllable
Osmosis
121
No energy, Yes Protein, Yes Specific, Controllable
Passive Transport (Facilitated)
122
Yes Energy, Yes Protein, Yes Specific, Contollable
Active Transport
123
Small molecules and water enter or leave the
cell through____________________
the lipid bilayer or by transport
proteins
124
Large molecules, such as polysaccharides and
proteins, cross the membrane via __________
vesicles
125
Fusion of separate regions of the lipid bilayer:
bilayers come into_________ and then
they ______
close apposition,
fuse
126
* transport large
molecules
Endocytosis and Exocytosis
127
Types of Endocytosis
*Pinocytosis
*Phagocytosis
*Receptor-mediated
endocytosis
128
cell brings in macromolecules and
particulate matter by forming new vesicles from the
plasma membrane
Endocytosis
129
*cell creates a
vesicle around a droplet of extracellular fluid
◦ non-specific process
Pinocytosis
130
Pinocytosis or also known as
Cell Drinking
131
Cell Eating
Phagocytosis
132
* Depends on the presence of receptor molecules
embedded in the cell membrane
* triggered when extracellular substances bind to special receptors, ligands, on the membrane
surface, especially near coated pits
* Upon binding of ligand, receptor-ligand complex
accumulate within coated pits (internalizes the
ligand)
* Formation of vesicle that pinches off into the
cytoplasm
Receptor-mediated endocytosis
133
*transport vesicle that
budded from the Golgi
apparatus is moved by
the cytoskeleton to
the plasma membrane
*when the two
membranes come in
contact, the bilayers
fuse and spill the
contents to the
outside
Exocytosis
134
Three main types
of intercellular
links:
-tight junctions,
-adhering junctions (zonula adherens,
desmosomes),
- gap junction
135
➢membranes of
adjacent cells
are fused,
forming
continuous belts
around cells
➢prevent leakage of extracellular fluid
across a layer of epithelial cells
Tight junction
136
➢fasten cells together
into strong sheets,
much like rivets
➢reinforced by
intermediate filaments
of keratin
➢attach muscle cells to
each other in a muscle
Desmosome (anchoring junctions)
137
➢provide cytoplasmic channels
between adjacent cells
➢salt ions, sugar, amino
acids, and other small
molecules can pass
Gap junction (communicating junctions)
138
every cell maintains
concentrations of inorganic solutes inside the
cell that are different from those outside the cell
Ionic steady state
139
* animal cell do not have rigid
walls and cannot resist any buildup of large intracellular pressure
* cells will change size when
placed in different concentrations
of impermeable substances
dissolved in water
Cell volume
140
osmotic movement of water
shrinkage or swelling
141
Two ways to prevent osmotic swelling
a. pump water out as fast as it leaks in
b. pump out solutes that leak into the cell – major mechanism for regulation of cell volume
142
membrane permeability to charged particles
depends both on the ________________ and on the ____________.
-membrane permeability constant
-electrical signal
143
Two Forces can act on charged atoms and
molecules to produce a net passive diffusion of
each species across a membrane:
Chemical Gradient and Electric Field
144
arising from differences
in the concentration of the substance on the
two sides of the membrane
chemical gradient
145
difference in electric potential
across the membrane
electric field
146
ion will move away from regions of ______________, and if that ion is positively charged it will also move toward ___________
-high concentration
-increasing negative potential
147
determined by the sum
of the combined forces of the concentration
gradient and electrical gradient
*Electrochemical gradient
148
potential at which
an ion is in electrochemical equilibrium
*Equilibrium potential
149
*Equilibrium potential
V or mV
150
ratio of the ion concentrations on opposite
sides of the membrane influence the________________
value of
the equilibrium potential
151
an ion species can passively diffuse against its
chemical concentration gradient if the electrical gradient (potential difference) across the membrane is in the___________ to and ________ the concentration gradient
- opposite direction
-exceeds
152
will not be
affected by electrical forces but by the
concentration gradient
uncharged molecules (sugar)
153
if diffusible solutes are separated by a
membrane that is freely permeable to water and
electrolytes but totally impermeable to one
species of ion, the diffusible solutes become
unequally distributed between the two
compartments.
Donnan Equilibrium
154
Cell is dead if _________________
Cell Membrane is not responsive
155
Diffusion is fast until equilibrium is reached
Dissolving in Lipid Phase
156
Diffusion/ Concentration slows down until equilibrium is reached
Diffusion through labile or fixed aqueous channel
157
Diffusion is very slow because the carrier is occupied, the diffusion will continue if the carrier is empty. This continues until equilibrium is reached
Carrier mediated transport (Facilitated or Active Transport)
158
Water pass through the membrane through ____________
Aquaporins
159
Process of Endocytosis
1. Invagination
2. Formation of Pouch
3. Formation of Vesicle
4. Lysosome Digest
5. Undigested molecules undergo exocytosis
160
Na+
Exterior: 120 mM
Interior: 10 mM
161
K+
Exterior: 2.5
Interior: 140
162
Ca2+
Exterior: 2.0
Interior: <10-3
163
Cl-
Exterior: 120
Interior: 3-4
164
A-
Interior: 140
